In the textile industry it is normal, for the washing and fulling of fabrics in rope form, to treat the fabrics in the shape of compressed folds.
The known method used to form these folds in the fabric and to compress the folds comprises continuously advancing the fabric toward an enclosure wherein it is retained, so that the fabric is progressively folded within the enclosure, and applying pressure to the folds thus formed. To this end two driven rollers, which exert a pressure toward each other, feed the fabric into the inside of a retaining box, the cross-section of which is square or rectangular shaped. Generally, the bottom and two sides of the retaining box are fixedly mounted, and the top is hingedly mounted so that it can move toward or away from the discharge opening of the retaining box.
The hinged top is urged by a pressure device to close the discharge outlet of the retaining box while the retaining box is filled with fabric in the form of folds which are compressed by an amount which is a function of the pressure exerted thereon by the hinged top on the fabric and of the degree of adherence between the fabric and the feeding rollers.
In the known retaining boxes of the fabric fulling and washing machines, there have been introduced mechanical devices provided with reciprocating movements, arranged in the bottom part of the retaining box, in order to compress the folds of the fabric in combination with the pressure exerted by the top.
However, in all the known devices the discharge of the fabric out of the retaining box takes place in an intermittent manner, since the feeding rollers must, in addition to feeding the fabric, compress the fabric, and overcome the opposing force or friction of the retaining mechanisms in the retaining box in order to ensure the continuity of the operation.
Accordingly, it will be apparent that if the pressure exerted by the hinged part of the retaining box is increased, there comes a moment at which the compressing feeding rollers slip on the fabric, thereby harming or damaging the fabric by abrasion. Such slippage is relatively easily produced due to the fact that the treatment is carried out in a wet state.
If the advancement speed of the fabric is increased, the delays in the operation of the device between the filling phases, the compressing phases and the discharge phases from the retaining box take place within a shorter cycle, until a limit is reached whereat the hinged part oscillates so fast that there is no time for either the folding of the fabric or the required compression of the fabric to take place. There even comes a moment at which the hinged part stabilizes itself in a balanced position whereat it effects small continuing oscillations.
If the volumetric capacity of the retaining box is increased, the friction of the fabric during its passage through the retaining box is proportionally increased. This makes it necessary to reduce the retention pressure applied by the hinged part until there is reached a balance stage at which neither slippage nor defects in the fabric are produced.
If the pressure between the feeding rollers, the surface of which should be hard, is excessively increased, the likelihood of flaws being produced in the fabric due to the compression of the fabric is also increased.